1. Field of the Invention
The present invention relates to a toner supply device and an image forming apparatus.
2. Discussion of the Background
Electrophotographic image forming apparatuses include a photoreceptor unit. The photoreceptor unit includes a photosensitive drum and a developing device. On the photosensitive drum, an electrostatic latent image is to be formed, and the developing device attaches toner to the photosensitive drum. Every formation of an image on a recording sheet of paper involves conveyance of a toner image formed on the photosensitive drum to the recording sheet of paper, and this reduces the toner in the developing device. In order to eliminate depletion of toner in the developing device, some of the image forming apparatuses are provided with a toner supply device to supply toner to the developing device.
Japanese Unexamined Patent Application Publication No. 9-015957 discloses a toner supply device that is disposed outside the image forming apparatus. In order to ensure toner conveyance ability to the developing device, the toner supply device uses an air pump to send air to a toner conveyance path provided with a conveyance screw. Japanese Unexamined Patent Application Publication No. 10-198152 discloses a toner cartridge (which corresponds to the toner supply device) that is integral with the developing device. In order to prevent pressure on the inside of the cartridge due to external air taken in by the developing device, the toner cartridge is provided with an air hole on a plug that is engaged with a side surface of a hopper that stores toner to be supplied to the developing device.
Japanese Unexamined Patent Application Publication No. 2000-047464 discloses a volume reducible toner container (which corresponds to the toner supply device). In order to ensure stable supply of toner stored in the toner container, the toner container is provided with an air supplier separate from a toner discharger. The air supplier accepts supply of air from an air pump. Japanese Unexamined Patent Application Publication No. 2004-012925 discloses a toner cartridge (which corresponds to the toner supply device) that is provided with an air hole on a connecting material connected to a toner conveyance member that conveys toner to the developing device.